The table saw is one of the most common and versatile pieces of woodworking equipment. A typical table saw consists of a saw blade mounted on an arbor and driven by a motor. The blade protrudes through the surface of a table, which provides support for the material being cut.
The depth of the cut often must be set precisely, particularly when cutting a dado or rabbet. In a typical table saw, the depth of the cut is varied by adjusting the blade height: the distance that the cutting edge of the blade protrudes above the table surface. The higher the blade protrudes above the surface, the deeper the cut. In some table saws, the blade and arbor are fixed and the table is moved up and down. In other table saws, the table is fixed and the blade and arbor are moved up and down. The angle of the cut is typically controlled by adjusting the angle of the blade relative to the table.
An operator may control the height of the blade by rotating a control handle, usually in the form of a disk or wheel, which drives a mechanism to lower or raise the saw blade relative to the table. The control handle is commonly mounted on an axle. Typically, table saws present no means for communicating the height of the blade above the table to the operator. Setting the blade height tends to be more difficult for table saws than other machine tools because the relationship between a given rotation of the control handle and a change in the blade height is not constant.
Commonly, the operator will measure the height of the saw blade using one of a variety of devices. One such device is a height gauge which functions much like a caliper, where one leg sits upon the surface of the table and the other sits upon the upper edge of the saw blade. The height is displayed on a dial. Another such device is a calibrated fence. A fence is a movable guide that is used to guide material to be cut through the saw blade. When the saw is stopped, the calibrated fence may be placed next to the blade and the height of the blade adjusted against a scale inscribed in the surface of the fence. Similar devices include scales, tape measures, or step blocks. It is common to have to make several adjustments to get precise results using these devices.
When using any of these devices, the saw must be stopped for the operator to safely read the height of the saw blade. Stopping the saw and applying an external measurement device to measure the height of the blade is both time consuming and prone to error. Furthermore, there is an incentive for an operator to sacrifice safety and adjust the saw blade while it is still spinning.
Another common method is to make a trial cut in a scrap piece of wood. Using this method, the operator makes repeated cuts in a scrap piece, making fine adjustments between each cut and measuring the result. This method is awkward, time consuming, and imprecise.
Accordingly, there is a need for an easy to use way to adjust the height of the saw blade accurately and to make fine height adjustments while the saw is spinning. Furthermore, any adjustment device should be inexpensive and easy to install.
The same needs exists for many machine tools, such as routers. In a table saw, the blade depth is directly related to the cutting depth. In other tools, the cutting depth is indirectly related to the distance from the cutting edge to the table, but the principle problems are the same. Throughout this specification, cutting depth and blade height are used interchangeably when referring to table saws.